1. Field of the Invention
The present invention relates to a data reading method and data reading apparatus used in a disk drive storage device such as a hard disk drive (HDD), and more particularly to a data reading method and data reading apparatus provided with a sector buffer having a caching function.
2. Description of Related Art
A memory referred to as a sector buffer is provided in disk drive apparatus. A common approach to speed up sequential reading in the disk drive is to continue reading in the following area (this is referred to as look-ahead) when the reading of an area requested by a read command has been completed. Sequential reading speed can thus be improved because when the next read command arrives the data will already be present in the sector buffer memory. The serial numbers assigned to usable sectors are referred to as logical block addresses (LBAs).
FIG. 7 is a diagram explaining the look-ahead operation, which illustrates reading from the disk and activity on the interface. The numbers in the drawing are addresses, and the arrows indicate the sequence of operations.
When the direction is forward, the existing method reads the specified data on the disk, then continues reading from the disk as long as there is space in the buffer memory. Accordingly, until a new read operation is performed, there will be data in the buffer memory, and that data can be transferred. This is a pre-fetch (look-ahead) operation. In the example in FIG. 7, when a first command (Read 10111 Length 3) is issued, the reading of the area (10111-10113) requested by the command is carried out from the disk with transfer on the interface. When the reading of the area requested by the read command has been completed, reading of the following area (10114----) continues.
Thus the read-cache process reads data that the host device commands to be read, or pre-fetches data predicted to be read in the future from the magnetic disk (look-ahead) and retains the data in a memory.
In conventional disk drives of this type, although sequential reading could be speeded up by look-ahead, no consideration was given to backward sequential reading. Thus, when backward sequential reading was performed, the operation of reading data from the disk would continue to be performed after the command arrived, with the problem that the processing took more time than for forward sequential reading.
This problem is heightened by the more recent use of disk drive storage devices such as HDDs for recording and editing video signals. Here, when the video signal is played in reverse, backward sequential reading is carried out on the HDD. Since backward reading performance is worse than in forward reading, the system must be designed on the basis of the backward sequential reading performance. When there is a large performance difference between backward sequential reading and forward reading, a design matched to the backward sequential reading performance underestimates the performance of the HDD, increasing the cost. If attempts are made to contain the cost, the stability of system operations cannot be guaranteed because backward reading margins are reduced.
Thus, it can be seen that there is a need in the art to provide a less expensive and highly reliable data reading method and apparatus that can improve backward sequential reading performance.